of Ssu72 inactivation (Fig. 4B). Finally, an in-tegrated b-globin gene construct with a SV40late PAS or mutated version (22) in human embry-onic kidney 293 cells displays a gene-loop con-formation with the wild type, but not the mutantPAS construct. Similarly we observed a threefoldincrease in the levels of divergent pncRNA withthe mutated PAS (Fig. 4C), indicating a similareffect in a mammalian system.